Certainly no secret. Both the 1st and 2nd Florida Cavalry (US) appear in Dyer's Compendium. Both units were comprised of Florida Unionists, at least some of whom came from the 15th Confederate Cavalry. I don't doubt that they cooperated with local guerilla bands.

Fred

1st Regiment Cavalry

Authorized by Gen. Banks October 29, 1863, and organized at Barrancas,
Fla., December, 1863, to August 1864. Attached to Pensacola, Fla., District
West Florida Dept. Gulf, to October, 1864. 2nd Brigade, District West
Florida, to January, 1865. 3rd Brigade, District West Florida, to March,
1865. 2nd Brigade, Lucas' Cavalry Division, Steele's Command, to May, 1865.
District of West Florida to November, 1865.

SERVICE.--Duty at Barrancas, Fla., until March, 1865 Expedition from
Barrancas toward Pollard, Ala., Jul 21-25, 1864. Actions at Camp Gonzales
July 22, and near Pollard July 23. Expedition from Barrancas August 13-14.
Expedition from Barrancas to Mariana September 18-October 4. Euche Anna C.
H. September 23. Mariana September 27. Vernon September 28. Expedition up
Blackwater Bay October 25-28. Milton October 26 Expedition from Barrancas
to Pine Barren Creek November 16-17. Pine Barren Creek and Bridge November
17. Expedition to Pollard, Ala., December 13-19. Bluff Springs and Pollard
December 15. Escanabia Bridge December 15-16. Pine Barren Ford December
17-18 Expedition from Barrancas to Milton February 22-25 1865. Milton
February 23. Campaign against Mobile and its defenses March 18-April 9.
March to Blakely Ala., March 18-31. (Dismounted men remain at Barrancas.)
Expedition to Alabama & Florida R. R. March 18-25. Near Evergreen March 24.
Muddy Creek, Ala. March 26. Siege of Fort Blakely March 31-April 9 Near
Blakely April 1. Occupation of Mobile April 12 March to Montgomery April
13-25. Duty there and in Alabama until May. Ordered to Barrancas, Fla., and
duty in Western and Middle Florida until November Mustered out November 17,
1865.

2nd Regiment Cavalry

Organized at Cedar Keys and Key West, Fla., December, 1863, to June, 1864.
Attached to District of Key West and Tortugas, Dept. of the Gulf, and Dept.
of Florida, to November, 1865.

SERVICE.--Duty at Fort Myers, Cedar Keys and in District of Key West until
June, 1865. Skirmishes at Pease Creek, Fla., February 13-14 and February
20, 1864. Attack on Fort Myers February 20. Affair at Tampa May 6.
Operations on West Coast of Florida July 1-31. Expedition to Bayport July
1-4. Skirmish at Station Four, near Cedar Keys, July 6. Expedition to St.
Andrews Bay July 20-29. Fort Myers August 26. Expedition to Bayport October
1, and to St. Andrews Bay October 20-29. Near Magnolia October 24.
Expedition to Otter Creek, on Florida R. R., October 30-31. Braddock's
Farm, near Welaka, February 5, 1865. Station Four, near Cedar Keys,
February 13. Attack on Fort Myers February 20. Operations near St. Marks
February 21-March 7. East River Bridge March 4-5. Newport Bridge March 5-6.
Natural Bridge March 6. Occupation of Tampa May 27. Duty in District of
Florida until November. Mustered out November 29, 1865.

Source - "A Compendium of the War of the Rebellion" by Frederick H. Dyer