For large file, TDP, VM and image full backups, they can ...
It depends on if it's small files or not. I normally have a small-file pool, which is the DIRMC, VMTLMC, and TOCDESTINATION. The offsite for this is kept reclaimed down to 1 tape, and I try to restore that primary pool first.
For large file, TDP, VM and image full backups, they can restore directly from tape, no problem.
For small files, block level incrementals, or instant restore, it depends on the number of tapes, number of drives and number of concurrent restores.
One restore with 6+ tape drives and it's not much of an issue.
Ten restores with 6 tape drives could be an issue.
This is where properly setting your RTO/RPO and tiers in advance matters.
Tier-0 would be your TSM server, the DIRCOPY/DIRPOOL, ESX hosts, switches, arrays, etc. You'd restore or rebuild these directly before anything else.
Tier-1 would be the things you can restore within the first couple of days. It would be in one collocation group or one storage pool. You could restore those first, direct from tape. It should only be a small number of systems, such as a NIM server, HR/Payroll, and inventory/medical tracking. Primary systems only.
Tier-2 systems would be what can be restored within a week or two. This might be direct from tape, or restore to disk first. It would be any other important systems that your company can run without, but which is a serious pain to go a long time. Generally, this would be under 50 systems. You wouldn't usually restore all of these at a normal DR test, but maybe a different subset at each DR test, just to make sure you *can* restore them.
Tier 3 might be the systems that you don't restore for a few months. Some might be rebuilt from production clones, and some might just restore a source tree for critical system development. Dev, QA, HA, and anything else that you can operate without, but which should eventually be taken care of. You probably won't ever restore this at a DR site, rather you'd wait until you fail back to new-production. If they were unrecoverable, they could be rebuilt, or decommissioned, without business risk.